Arrangement for preventing glow discharges between insulated conductors in generator end turns



Aprll 21, 1970 UMKYULL ET AL 3,508,096 ARRANGEMENT FOR PREVENTING GLOWDISCHARGES Q BETWEEN INSULATED CONDUCTORS IN GENERATOR END TURNS FiledNov. 25, 1968 3mm Ulrich ku LL RoLa Incl 50H u Ler- A M' U,J-QA%ME FAQUnited States Patent Filed Nov. 25, 1968, Ser. No. 778,424 Claimspriority, application Switzerland, Dec. 5, 1967, 17,035/ 67 Int. 'Cl.H0211 3/40 US. Cl. 310-196 4 Claims ABSTRACT OF THE DISCLOSURE Anarrangement for preventing glow discharges between two insulatedelectrical conductors having diflFerent potentials, particularly at theend turn portions of windings of high voltage rotary electricalmachines, utilizes conductive layers embedded in the insulation of thetwo conductors where they approach one another in the end turn area andthese conductive layers are electrically interconnected. Semiconductorlayers are also embedded in the insulation and surround the windingconductors as well as the contact the conductive layers, andsemiconductor layers are also applied to the exterior surfaces of theinsulation. Intermediate supporting and spacing elements ofsemiconductive material reinforced with glass fiber are provided in theair gap between conductors.

responding to the line or rated voltage of the machine.

During a voltage test, the full test voltage occurs at these points.Since, however, the distance between the conductors at the end turns ofthe winding cannot be appreciably increased for constructional reasons,it is possible that already at the normal operating voltage dischargescan occur in the air or gas gaps at the phase separation points whichunder certain circumstances can be very undesirable. With conventionalconstructions this is often avoided by filling the space between thephases at the separation points with a semiconductive mass, whereby inmost cases the filling material also serves as a mechanical supportingelement.

By filling the space between the end turn parts of the coils with such amass, which generally consists of a material for instance glass fibre,which is saturated with a semiconductive varnish, it is possible toobtain a very small conductor spacing but such a filling is not verydurable. This is due to the fact that it is impossible to produce afilling of this kind which is free of cavities and furthermore as aresult of the shrinkage which occurs when the filling masses hardens,vibrations result between the conductor insulation and the filling sothat the latter becomes brittle and fine cracks occur. The gradualdestruction of the filling mass due to glow discharges is bound toaffect its mechanical strength, so

that it can no longer also act as a supporting element.

As a result of the continuously increasing size of modern machines withcorrespondingly higher voltage ratings, it has become necessary toprovide a device which prevents glow discharges between two insulatedconductors of dilferent voltage potential, particularly with rotatingmachines having a high rated voltage. In accordance with the inventionthis is achieved by providing an electrically conductive layer in thecritical region at least on the opposite sides of the conductors, thislayer being located within the conductor insulation, the surface ofwhich is covered on all sides with semiconductive glow dischargeprotection layers, the conductive layers being connected togetherelectrically and-at least their edges being covered with an additionalsemiconductive coating.

A constructional example of the invention is explained by means of theaccompanying drawings wherein:

FIGURE 1 shows the phase separation point of two bar conductors in theend turn part of a generator winding in longitudinal section, and

FIGURE 2 shows the same bar conductors in a crosssectional view takenalong the line AA of FIGURE 1.

With reference now to the drawings, at least the opposite broad sides ofthe end turn part of two neighboring conductor bars 1 are provided atthe phase separation point with conductive layers 2 which are mostexpediently in the form of a coating of varnish. These layers 2 belowthe surface of the conductor insulation 4 extend in the longitudinaldirection up to the points where the bars begin to diverge, that is tosay the layers in this example lie in the critical region between bothbends in the end turn part of the winding where the parallel bars comevery near to each other. The edges of the layers 2 are covered on allsides with a semiconductive coating 3 which in the critical region alsosurrounds the bar inside the insulation. The conductive layers 2 as wellthe semiconductive layers 3 are produced when the usual insulation layer4 is applied to the conductor, for instance by means of coatings or theinsertion of suitable thin foils, whereupon a semiconductive layer 5which acts as a protection against glow discharges is also applied tothe outside of this insulation.

The conductive layers 2 are connected together bymeans of electricallyconductive contact strips 6 and an intermediate supporting element 7located in the gas gap. This supporting element 7 which for instanceconsists of a semiconductive synthetic material reinforced with glassfibre also serves as a spacer for the bars. Since the capacity betweenthe conductive layers 2 and the conductor copper of both bars 1 isapproximately equal, the voltage of the layers 2 and of the intermediatepart of the insulation and the gas gap is reduced to half the voltagebetween the conductors of both bars 1. The layer of insulation 4 on theouter side which is provided with a semiconductive protective layer 5serves solely to control the voltage build-up at the edges of the layerson the surface of the bars so as to prevent the occurrence of glowdischarges.

With the arrangement described above, a suitable voltage control enablesthe gas gaps at the phase separation points to be completely relieved ofall electrical stresses because these are now transferred to theconductor insulation which can withstand glow discharges. In this way itis possible to obtain minimum spacing between the conductors at thephase separation points and also an improvement as regards fiowdischarges during voltage tests. The supports for the coil end turnshave a constant mechanical strength and operational safety is increased.Finally, cooling is also improved because the gas gaps are no longerfilled with a semiconductive mass.

We claim:

1. An arrangement for preventing glow discharges between two insulatedelectrical conductors having different potentials, and particularly atthe end turn portions of windings of high voltage rotary electricalmachines comprising conductive layers embedded in the insulation of thetwo conductors where they approach one another in the end turn area,means interconnecting said conductive layers, semiconductive glowdischarge protecti ve layers also embedded in the insulation andsurrounding said conductors at the location of said conduc-r tivelayers, and semiconductor layers surrounding the insulations on saidconductors.

2. The invention as defined in claim 1 wherein said meansinterconnecting said conductive layers includes conductive strips whichpass through the insulation of the conductors.

3. The invention as defined in claim 1 wherein said meansinterconnecting said conductive. layers is comprised of conductivestrips which pass through the insulation of the conductors, and anelectrically conductive supporting element located between theconductors.

4. The invention as defined in claim 3 wherein said electricallyconductive supporting element between said conductors is comprised ofglass fiber reinforced semiconductor synthetic material.

References Cited UNITED STATES PATENTS WARREN E. RAY, Primary Examiner

